decrease tolerance on serialization check for macos test builds

[imatiach-msft]

The nightly build is failing for macos platform due to tolerance checks in serialization backcompat test.
This PR decreases the tolerance in the check to fix the macos tests.

[codecov-commenter]

Codecov Report

Merging #496 (769e5f0) into master (3f1e586) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #496   +/-   ##
=======================================
  Coverage   86.62%   86.62%           
=======================================
  Files          62       62           
  Lines        4046     4046           
=======================================
  Hits         3505     3505           
  Misses        541      541           

Flag	Coverage Δ
unittests	86.62% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 3f1e586...769e5f0. Read the comment docs.